1. Field of the Invention
The present invention is directed to a method for intensity norming of an optical sensor for measuring a periodically fluctuating electrical and/or magnetic field strength.
2. Description of the Related Art
A known example of an optical sensor for measuring electrical and magnetic fields is a two-channel, polarimetric optical alternating current and/or alternating voltage sensor. Such sensors proceed, for example, U.S. Pat. No. 4,564,754, German Patent Document DE-A-4 432 146 and U.S. Pat. No. 4,894,608.
Such a sensor utilizes the fact that, when polarized light is sent through an electrical and/or magnetic field, a modification of the polarization condition of the light which is dependent on the field strength of this field is produced due to specific physical effects (for example, Faraday effect, Pockels effect) and can be measured.
Alternating current and alternating voltage generate an electrical and/or magnetic field of periodically fluctuating field strength in their environment that generates a periodic fluctuation of the polarization condition of the polarized light sent through this field.
"Two-channel" in the known sensor means that the polarized light sent through the field is supplied to a polarization beam splitter that divides the supplied light into two light components of respectively fixed polarization conditions that, however, are different from one another, for example orthogonal relative to one another, whose intensities are dependent on the polarization condition of the light sent through the field and supplied to the divider.
Every light component generated in this way thus forms an intensity signal whose intensity is dependent on the field strength of the field. What is to be understood here as intensity signal is not only the light component itself but any other generated signal whose intensity, like the intensity of a light component varies dependent on the field strength of the field to be measured. An example is the electrical intensity signal generated by an opto-electrical transducer, for example a diode, from a light component.
Apart from attenuation losses, the intensities of the two light components that have arisen or of the intensity signals add up to the intensity of the light sent through the field and supplied to the polarization beam splitter. When the intensity of this supplied light is constant, the sum of the intensities of the two light components or intensity signals is also constant.
In order to eliminate influences of a non-constant intensity of the light sent through the field and supplied to the polarization beam splitter, an intensity norming is usually implemented.
A standard method for intensity norming of an optical sensor for measuring electrical and magnetic fields is the minus/plus division, i.e. a quantity is formed from the two light components or intensity signals that corresponds to a difference between the intensities of the two light components divided by the sum of the intensities of the two light components (see, for example, U.S. Pat. No. 4,564,754).
The minus/plus division is in the position to also compensate an intensity of the light sent through the field and supplied to the polarization beam splitter that fluctuates very rapidly.
Due to the periodically fluctuating polarization condition of the light sent through the field and supplied to the polarization beam splitter that is conditioned by the field strength, the intensities of the two light components or of both intensity signals generated by the splitter respectively exhibit a corresponding, periodic fluctuation, i.e. they are composed of a constant intensity part this is and of an intensity part periodically fluctuating dependent on the measured field strength.
The periodically fluctuating intensity parts of the intensities of the two light components generated by the splitter or of both intensity signals are in anti-phase relative to one another and, in the ideal case, exhibit an amplitude of the same amount, this resulting therein that the sum of the periodically fluctuating intensity parts of both light components or intensity signals is also constant in addition to the sum of the constant intensity parts when the intensity of the light sent through the field and supplied to the polarization beam splitter is constant.
In the real case, however, the sum of the intensities of the two light components generated by the splitter or of the two intensity signals is often not constant but fluctuates periodically even given a constant intensity of the light sent through the field and supplied to the polarization beam splitter.
This occurs, for example, when the intensity parts of the intensities of thetwo light components generated by the polarization beam splitter or of the two intensity signals that fluctuate periodically in anti-phase relative to one another exhibit amplitudes of an amount differing from one another.
This, for example, can be based thereon that a light conductor conducting the one generated light component from the polarization beam splitter to, for example, an opto-electrical transducer for conversion of the intensity of this light component into a corresponding electrical intensity signal, for example an optical fiber, exhibits a different attenuation than a light conductor conducting the other generated light component to an opto-electrical transducer for conversion of the intensity of this other light component into a corresponding electrical intensity signal.
A standard method for intensity norming of an optical sensor for measuring electrical and magnetic fields that is different from the minus/plus division that is known as AC/DC division (see, for example, U.S. Pat. No. 4,894,608) can compensate light components generated by the polarization beam splitter and containing such intensity parts with amplitudes of a different amount which are periodically fluctuating relative to one another in anti-phase or, respectively, corresponding intensity signals. This method, however, fails given rapid fluctuations of the intensity of the light sent through the field.